The overall objective of the proposed research is to elucidate in molecular terms the mechanism by which interferon acts to affect a wide variety of fundamental viral and cellular processes. The specific aims and methods are: (1) To further purify the interferon-induced ribosome-associated protein kinase(s) that possess translational inhibitory activity and catalyze the phosphorylation of ribosome-associated Pl and the alpha subunit of initiation factor eIF-2; to purify the phosphoprotein phospatases(s) that catalyze the selective dephosphorylation of Pl and eIF-2 alpha, and then to determine to biochemical and biophysical properties of the purified proteins. The kinase is greatly enhanced in murine cells by interferon; the phosphatases are found in interferon-treated and untreated cells at comparable levels. (2) To elucidate the precise biochemical mechanism(s) by which the translation of viral messenger RNA in vitro, and in vivo, is inhibited by the interferon-mediated inhibitor; these inhibitors include the interferon-induced ribosome-associated protein kinase, and the ribonuclease enhanced by 2',5'-oligoadenylate, the product of the interferon-induced oligonucleotide synthetase. (3) To resolve whether the activity of the host-coded interferon-mediated inhibitors is directed specifically toward all viral messenger RNAs with comparable efficiency, or whether the accumulation and translation of certain classes of viral as well as some cellular messenger RNAs are selectively affected by the interferon-mediated inhibitors, and to elucidate the molecular basis of the mRNA sensitivity to interferon action. (4) To elucidate the molecular basis of the differential effect of interferon on the expression of the early region of the simian virus 40 genome in virus-infected CV-1 cells as compared to virus-transformed 3T3 cells: and to compare the mode of action of interferon in reovirus-infected and SV40-infected cells.